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Photonics studies and engineers the generation, transport, manipulation and detection of light. A photonic system may combine a laser, optical waveguides, modulators and photodetectors to carry information or measure a physical quantity.

An optical communication link illustrates the chain: a source produces light, a modulator encodes a signal, a waveguide transports it, and a detector converts received photons into an electrical response. Wavelength, polarization and phase can provide different information channels. Loss and detector noise determine how much of the encoded information is recoverable, so moving a signal optically does not remove the need for a quantitative signal model.

Rüdiger Paschotta develops technical explanations of photonics through the RP Photonics Encyclopedia by Rüdiger Paschotta. Its treatment of refractive index distinguishes the phase velocity of a monochromatic wave from the propagation of a pulse envelope. Because the index depends on frequency, the two velocities generally differ; this dispersion matters when predicting pulse delay and broadening. The explanation connects a material parameter used in optical design with a measurable propagation process.^[ref]